1. Field of the Invention
This invention relates to spandex having low tackiness and, more particularly, to spandex having dispersed therein effective amounts of an anti-tack additive.
2. Description of the Background Art
Spandex is known to be tacky. This is especially important in wound packages of dry-spun spandex, where the pressure can be very high due to "package relaxation", which is the recovery of the filament from the stretch it experiences during spinning. The high pressure can make it especially difficult to remove and use filament near the core of the package, where conditions are most extreme. Time and temperature contribute to tackiness, so that wound packages of spandex that have been stored, for example for months, experience significantly more core waste than freshly spun and wound packages. Reducing the tackiness and the resulting waste would improve the economics of spandex filament production. Steps taken to reduce tack, however, should not interfere with the continuity of the dry-spinning process by which spandex is made.
U.S. Pat. No. 4,296,174 discloses the incorporation of metal salts of fatty acids such as calcium stearate into dry-spun spandex to reduce the tackiness of the spandex. However, such additives are problematic in the dry-spinning process, creating deposits within the spinneret capillaries and plugging filters in the polymer solution lines. These effects are detrimental to spinning continuity, i.e. when the capillaries or filters become plugged, the continuous filament production is interrupted and the process must be stopped to clean out the plugging deposits or replace the plugged parts with clean ones. An anti-tack additive with a combination of good dry-spinning processibility and anti-tack characteristics is still desired.
Japanese Patent Application Publication Number 1-298259 ("JP '259") discloses a method for producing thermoplastic polyurethane elastic nonwoven fabric by melt-extruding and melt-blowing thermoplastic polyurethane which has been blended with 0.1-2.0 wt % of a compound represented by the formula: EQU (C.sub.n H.sub.2n+1).sub.m X
wherein n is 15 to 35; m is 1 to 3; and X is a fatty acid ester having 5 or less carbons, a fatty amide having 5 or less carbons, or a fatty acid ester having 5 or less carbons that includes a calcium salt. In this method, the thermoplastic resin is melt-spun and simultaneously powerfully impacted by a high-temperature, high-speed gas discharged from adjoining gas jets which blasts apart the melt-spun fibers into ultrafine fibers which are then collected on a moving plate thereby giving a nonwoven sheet. The sheet can be unrolled after having been rolled up. In the Description of the Prior Art, JP '259 teaches the undesirability of polyurethane elastic fiber production by dry spinning, as disclosed in Japanese Patent Application Publication No. 52-81,177. An anti-tack additive for dry-spun polyurethane fiber is still desired.
U.S. Pat. No. 3,382,202 discloses an additive system to impart substantially non-blocking and non-tacky characteristics to formed polyurethane structures. The additive system consists essentially of (1) about 0.5 to 4.0 parts of certain amides and bis-amides derived from fatty acids, including ethylene bis-stearamide and stearamide, and (2) about 1 to 15 parts of a finely divided inert particulate solid such as diatomaceous earth, silica, talc, feldspar, mica, carbon black, calcium bicarbonate, or sodium bicarbonate. An anti-tack additive that does not require a second inert component is still desired.